Brewster County is a county located in western part of the US state of Texas, along the border with Mexico. It is one of the nine counties that comprise the Trans-Pecos region of West Texas. As of the 2000 census, the population is 8,866. In 2009, the population was estimated to be 9,481. Its county seat and only city is Alpine. It is the largest county in Texas in land area.

Brewster County is named for Colonel Henry Percy Brewster, a Secretary of War for the Republic of Texas. During the American Civil War, Brewster served on the staffs of the two highest ranking Texans in the Confederate Army, General Albert S. Johnston and General John B. Hood.

The county is the largest in the state, over three times the size of the state of Delaware, and more than 500 sqmi (1295 km2) bigger than Connecticut.